Euv lithography apparatus

ABSTRACT

An extreme ultra violet (EUV) light source apparatus includes a metal droplet generator, a collector mirror, an excitation laser inlet port for receiving an excitation laser, a first mirror configured to reflect the excitation laser that passes through a zone of excitation, and a second mirror configured to reflect the excitation laser reflected by the first mirror.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/460,142 filed Aug. 27, 2021, now U.S. Pat. No. 11,605,477, the entirecontent of which is incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs.

For example, the need to perform higher resolution lithography processesgrows. One lithography technique is extreme ultraviolet lithography(EUVL). EUVL employs scanners using light in the extreme ultraviolet(EUV) region, having a wavelength of about 1-100 nm. Some EUV scannersprovide 4×reduction projection printing, similar to some opticalscanners, except that the EUV scanners use reflective rather thanrefractive optics, i.e., mirrors instead of lenses. One type of EUVlight source is laser-produced plasma (LPP). LPP technology produces EUVlight by focusing a high-power laser beam onto small tin droplet targetsto form highly ionized plasma that emits EUV radiation with a peakmaximum emission at 13.5 nm. The EUV light is then collected by an LPPcollector and reflected by optics towards a lithography target, e.g., awafer. The LPP collector is subjected to damage and degradation due tothe impact of particles, ions, radiation, and most seriously, tindeposition.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a schematic view of an extreme ultraviolet (EUV) lithographysystem with a laser produced plasma (LPP) EUV radiation source,constructed in accordance with some embodiments of the presentdisclosure.

FIG. 1B is a schematic view of an EUV lithography system exposure toolaccording to embodiments of the disclosure.

FIG. 1C schematically illustrates a device for synchronizing thegeneration of excitation pulses with the arrival of the target dropletsin the zone of excitation in accordance with an embodiment of thepresent disclosure.

FIG. 2 shows a schematic configuration of an LPP EUV radiation sourceaccording to an embodiment of the present disclosure.

FIG. 3 shows a diagram explaining a reuse of excitation laser accordingto an embodiment of the present disclosure

FIGS. 4A, 4B, 4C, 4D and 4E show configurations of mirrors in accordancewith various embodiments of the present disclosure.

FIG. 5 shows a flowchart of a method of making a semiconductor device,and FIGS. 6A, 6B, 6C and 6D show a sequential manufacturing operation ofthe method of making a semiconductor device in accordance withembodiments of present disclosure.

FIG. 7 illustrates a flow diagram of a process for operating an LPP EUVradiation source apparatus in accordance with some embodiments of thedisclosure.

FIG. 8 shows a control system for operating an LPP EUV radiation sourceapparatus in accordance with some embodiments of the present disclosure.

FIGS. 9A and 9B illustrate an apparatus for operating an LPP EUVradiation source apparatus in accordance with some embodiments of thepresent disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity. In the accompanying drawings, some layers/features may beomitted for simplification.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” Further, inthe following fabrication process, there may be one or more additionaloperations in between the described operations, and the order ofoperations may be changed. In the present disclosure, the phrase “atleast one of A, B and C” means either one of A, B, C, A+B, A+C, B+C orA+B+C, and does not mean one from A, one from B and one from C, unlessotherwise explained.

The present disclosure is generally related to an extreme ultraviolet(EUV) lithography system, apparatus and methods. More specifically, thepresent disclosure is directed to an apparatus to improve efficiency ofan excitation laser usage and to locally heat a vessel and/or parts of alaser produced plasma EUV source apparatus.

FIG. 1A is a schematic and diagrammatic view of an EUV lithographysystem 101. The EUV lithography system 101 includes an EUV radiationsource apparatus 100 to generate EUV light, an exposure tool 200, suchas a scanner, and an excitation laser source apparatus 300. As shown inFIG. 1A, in some embodiments, the EUV radiation source apparatus 100 andthe exposure tool 200 are installed on a main floor MF of a clean room,while the excitation source apparatus 300 is installed in a base floorBF located under the main floor. Each of the EUV radiation sourceapparatus 100 and the exposure tool 200 are placed over pedestal platesPP1 and PP2 via dampers DP1 and DP2, respectively. The EUV radiationsource apparatus 100 and the exposure tool 200 are coupled to each otherby a coupling mechanism, which may include a focusing unit.

The lithography system is an extreme ultraviolet (EUV) lithographysystem designed to expose a resist layer by EUV light (or EUVradiation). The resist layer is a material sensitive to the EUV light.The EUV lithography system employs the EUV radiation source apparatus100 to generate EUV light, such as EUV light having a wavelength rangingbetween about 1 nm and about 100 nm. In one particular example, the EUVradiation source 100 generates an EUV light with a wavelength centeredat about 13.5 nm. In the present embodiment, the EUV radiation source100 utilizes a mechanism of laser-produced plasma (LPP) to generate theEUV radiation.

The exposure tool 200 includes various reflective optic components, suchas convex/concave/flat mirrors, a mask holding mechanism including amask stage, and wafer holding mechanism. The EUV radiation EUV generatedby the EUV radiation source 100 is guided by the reflective opticalcomponents onto a mask secured on the mask stage. In some embodiments,the mask stage includes an electrostatic chuck (e-chuck) to secure themask. Because gas molecules absorb EUV light, the lithography system forthe EUV lithography patterning is maintained in a vacuum or a lowpressure environment to avoid EUV intensity loss.

FIG. 1B is a simplified schematic diagram of the exposure tool 200according to an embodiment of the disclosure showing the exposure ofphotoresist coated substrate 211 with a patterned beam of EUV light. Theexposure tool 200 is an integrated circuit lithography tool such as astepper, scanner, step and scan system, direct write system, deviceusing a contact and/or proximity mask, etc., provided with one or moreoptics 205 a, 205 b, for example, to illuminate a patterning optic, suchas a reticle 205 c, with a beam of EUV light, to produce a patternedbeam, and one or more reduction projection optics 205 d, 205 e, forprojecting the patterned beam onto the substrate 211. The one or moreoptics 205 a, 205 b provide the beam of EUV light with a desiredcross-sectional shape and a desired angular distribution. The reticle205 c is protected by a pellicle (not shown), which is held in place bya pellicle frame (not shown). The reticle 205 c reflects and patternsthe beam of EUV light.

Returning to FIG. 1B, following reflection from the reticle thepatterned beam of EUV light is provided to the one or more optics 205 d,205 e and is in turn projected onto the substrate 211 held by amechanical assembly (e.g., substrate table (not shown)). In someembodiments, the one or more optics 205 d, 205 e apply a reductionfactor to the radiation beam, forming an image with features that aresmaller than corresponding features on the reticle. The mechanicalassembly may be provided for generating a controlled relative movementbetween the substrate 211 and reticle 205 c.

The EUV lithography system may, for example, be used in a scan mode,wherein the chuck and the mechanical assembly (e.g., substrate table)are scanned synchronously while a pattern imparted to the radiation beamis projected onto the substrate 211 (i.e. a dynamic exposure). Thevelocity and direction of the substrate table relative to the chuck isdetermined by the demagnification and image reversal characteristics ofthe exposure tool 200. The patterned beam of EUV radiation that isincident upon the substrate 211 comprises a band of radiation. The bandof radiation is referred to, as an exposure slit. During a scanningexposure, the movement of the substrate table and the chuck is such thatthe exposure slit travels over an exposure field of the substrate 211.As further shown in FIG. 1B, the EUVL tool includes an EUV radiationsource 100 including plasma at ZE (zone of excitation) emitting EUVlight in a chamber 105 that is collected and reflected by a collector110 along a path into the exposure tool 200 to irradiate the substrate211. The zone of excitation (ZE) is a predetermined area where the metal(tin) droplet is irradiated by the excitation laser.

As used herein, the term “optic” is meant to be broadly construed toinclude, and not necessarily be limited to, one or more components whichreflect and/or transmit and/or operate on incident light, and includes,but is not limited to, one or more lenses, windows, filters, wedges,prisms, grisms, gratings, transmission fibers, etalons, diffusers,homogenizers, detectors and other instrument components, apertures,axicons and mirrors including multi-layer mirrors, near-normal incidencemirrors, grazing incidence mirrors, specular reflectors, diffusereflectors and combinations thereof. Moreover, unless otherwisespecified, the term “optic,” as used herein, is not meant to be limitedto components which operate solely within one or more specificwavelength range(s) such as at the EUV output light wavelength, theirradiation laser wavelength, a wavelength suitable for metrology or anyother specific wavelength.

In the present disclosure, the terms mask, photomask, and reticle areused interchangeably. In the present embodiment, the mask is areflective mask. One exemplary structure of the mask includes asubstrate with a suitable material, such as a low thermal expansionmaterial or fused quartz. In various examples, the material includesTiO₂ doped SiO₂, or other suitable materials with low thermal expansion.The mask includes multiple reflective multiple layers deposited on thesubstrate. The multiple layers include a plurality of film pairs, suchas molybdenum-silicon (Mo/Si) film pairs (e.g., a layer of molybdenumabove or below a layer of silicon in each film pair). Alternatively, themultiple layers may include molybdenum-beryllium (Mo/Be) film pairs, orother suitable materials that are configurable to highly reflect the EUVlight. The mask may further include a capping layer, such as ruthenium(Ru), disposed on the ML for protection. The mask further includes anabsorption layer, such as a tantalum boron nitride (TaBN) layer,deposited over the multiple layers. The absorption layer is patterned todefine a layer of an integrated circuit (IC). Alternatively, anotherreflective layer may be deposited over the multiple layers and ispatterned to define a layer of an integrated circuit, thereby forming anEUV phase shift mask.

In the present embodiments, the semiconductor substrate is asemiconductor wafer, such as a silicon wafer or other type of wafer tobe patterned. The semiconductor substrate is coated with a resist layersensitive to the EUV light in the present embodiment. Various componentsincluding those described above are integrated together and are operableto perform lithography exposing processes.

The lithography system may further include other modules or beintegrated with (or be coupled with) other modules. As shown in FIG. 1A,the EUV radiation source 100 includes a target droplet generator 115 anda LPP collector 110, enclosed by a chamber 105. The target dropletgenerator 115 generates a plurality of target droplets DP. In someembodiments, the target droplets DP are tin (Sn) droplets. In someembodiments, the tin droplets each have a diameter about 30 microns(μm). In some embodiments, the tin droplets DP are generated at a rateabout 50 droplets per second and are introduced into a zone ofexcitation ZE at a speed about 70 meters per second (m/s). Othermaterial can also be used for the target droplets, for example, a tincontaining liquid material such as eutectic alloy containing tin orlithium (Li).

The excitation laser LR2 generated by the excitation laser sourceapparatus 300 is a pulse laser. In some embodiments, the excitationlaser includes a pre-heat laser and a main laser. The pre-heat laserpulse is used to heat (or pre-heat) the target droplet to create alow-density target plume, which is subsequently heated (or reheated) bythe main laser pulse, generating increased emission of EUV light. Invarious embodiments, the pre-heat laser pulses have a spot size about100 μm or less, and the main laser pulses have a spot size about 200-300μm.

The laser pulses LR2 are generated by the excitation laser source 300.The laser source 300 may include a laser generator 310, laser guideoptics 320 and a focusing apparatus 330. In some embodiments, the lasergenerator 310 includes a carbon dioxide (CO2) or a neodymium-dopedyttrium aluminum garnet (Nd:YAG) laser source. The laser light LR1generated by the laser generator 300 is guided by the laser guide optics320 and focused into the excitation laser LR2 by the focusing apparatus330, and then introduced into the EUV radiation source 100.

The laser light LR2 is directed through an inlet port 102 including awindow (or a lens) into the zone of excitation ZE. The windows adopt asuitable material substantially transparent to the laser beams. Thegeneration of the pulse lasers is synchronized with the generation ofthe target droplets. As the target droplets move through the excitationzone, the pre-pulses heat the target droplets and transform them intolow-density target plumes. A delay between the pre-pulse and the mainpulse is controlled to allow the target plume to form and to expand toan optimal size and geometry. When the main pulse heats the targetplume, a high-temperature plasma is generated. The plasma emits EUVradiation EUV, which is collected by the collector mirror 110. Thecollector 110 has a reflective surface that reflects and focuses the EUVradiation for the lithography exposing processes. In some embodiments, adroplet catcher (or a tin bucket) 120 is installed opposite the targetdroplet generator 115. The droplet catcher 120 is used for catchingexcess target droplets. For example, some target droplets may bepurposely missed by the laser pulses.

In some embodiments, the EUV radiation source 101 includes a laserscatterer or reflector 190 including one or more EUV optics to scatteror reflect the excitation laser LR2 after the excitation laser hits thetarget droplet and/or the misses the target droplet, thereby preventingthe excitation laser LR2 from hitting EUV optics, such as the mirror 205a.

The collector 110 includes a proper coating material and shape tofunction as a mirror for EUV collection, reflection, and focusing. Insome embodiments, the collector 110 is designed to have an ellipsoidalgeometry. In some embodiments, the coating material of the collector 110is similar to the reflective multilayer of the EUV mask. In someexamples, the coating material of the collector 110 includes multiplelayers (such as a plurality of Mo/Si film pairs) and may further includea capping layer (such as Ru) coated on the multiple layers tosubstantially reflect the EUV light. In some embodiments, the collector110 further includes a grating structure designed to effectively scatterthe laser beam directed onto the collector 110. For example, a siliconnitride layer is coated on the collector 110 and is patterned to have agrating pattern in some embodiments.

In such an EUV radiation source apparatus, the plasma caused by thelaser application creates physical debris, such as ions, gases and atomsof the droplet, as well as the desired EUV radiation. It is necessary toprevent the accumulation of material on the collector 110 and also toprevent physical debris from exiting the chamber 105 and entering theexposure tool 200.

As shown in FIG. 1A, in some embodiments, a buffer gas is supplied froma first buffer gas supply 130 through the aperture in collector 110 bywhich the pulse laser is delivered to the tin droplets. In someembodiments, the buffer gas is H₂, He, Ar, N₂, or another inert gas. Incertain embodiments, H₂ is used as H radicals generated by ionization ofthe buffer gas can be used for cleaning purposes. The buffer gas canalso be provided through one or more second buffer gas supplies 135toward the collector 110 and/or around the edges of the collector 110.Further, the chamber 105 includes one or more gas outlets 140 so thatthe buffer gas is exhausted outside the chamber 105.

Hydrogen gas has low absorption to the EUV radiation. Hydrogen gasreaching to the coating surface of the collector 110 reacts chemicallywith a metal of the droplet forming a hydride, e.g., metal hydride. Whentin (Sn) is used as the droplet, stannane (SnH₄), which is a gaseousbyproduct of the EUV generation process, is formed. The gaseous SnH₄ isthen pumped out through the outlet 140. However, it is difficult toexhaust all gaseous SnH₄ from the chamber and to prevent the SnH₄ fromentering the exposure tool 200.

To trap the SnH₄ or other debris, one or more debris collectionmechanisms or devices 150 are employed in the chamber 105. As shown inFIG. 1A, one or more debris collection mechanisms or devices 150 aredisposed along optical axis A1 between the zone of excitation ZE and anoutput port 160 of the EUV radiation source 100.

FIG. 1C schematically illustrates a device for synchronizing thegeneration of excitation pulses with the arrival of the target dropletsin the zone of excitation used in the EUV lithography system illustratedin FIGS. 1A and 1B, in accordance with an embodiment. In an embodiment,a droplet illumination module (DIM) 410 is used for illuminating atarget droplet DP ejected from the nozzle 117. The droplet illuminationmodule 410 is focused at a fixed position P along the path of the targetdroplet DP from the nozzle 117 to the zone of excitation ZE. One ofordinary skill in the art will appreciate that once the excitation laserhits the target droplet DP within the zone of excitation ZE, the plasmaformed because of ionization of the target droplet DP expands rapidly toa volume that is dependent on the size of the target droplet and theenergy provided by the excitation laser. In various embodiments, theplasma expands several hundred microns from the zone of excitation ZE.As used herein, the term “expansion volume” refers to a volume to whichplasma expands after the target droplets are heated with the excitationlaser. Thus, the position P is fixed to be outside the expansion volumeto avoid interference from the plasma. In an embodiment, the position Pis fixed at a known distance, d, of several millimeters away from thezone of excitation ZE.

The droplet illumination module 410 is a continuous wave laser in anembodiment. In other embodiments, the droplet illumination module 410 isa pulsed laser. The wavelength of the droplet illumination module 410 isnot particularly limited. In an embodiment, the droplet illuminationmodule 410 has a wavelength in the visible region of electromagneticspectrum. In some embodiments, the droplet illumination module 410 has awavelength of about 1070 nm. In various embodiments, the dropletillumination module 410 has an average power in the range from about 1 Wto about 50 W. For example, in an embodiment, the droplet illuminationmodule 410 has an average power of about 1 W, about 5 W, about 10 W,about 25 W, about 40 W, about 50 W, or any average power between thesevalues. In some embodiments, the droplet illumination module 410generates a beam having a uniform illumination profile. For example, inan embodiment, the droplet illumination module 410 creates a fan-shapedlight curtain having substantially the same intensity across itsprofile. The beam produced by the droplet illumination module 410 has awidth in the range of about 10 μm to about 300 μm in variousembodiments.

As the target droplet DP passes through the beam generated by thedroplet illumination module 410, the target droplet DP reflects and/orscatters the photons in the beam. In an embodiment, the target dropletDP produces a substantially Gaussian intensity profile of scatteredphotons. The photons scattered by the target droplet DP are detected bya droplet detection module (DDM) 420 (interchangeably referred to hereinas “droplet detector 420”). The center of the target droplet DPcorresponds to the peak of the intensity profile detected at the dropletdetection module 420. In some embodiments, the droplet detection module420 is a photodiode and generates an electrical signal upon detectingthe photons reflected and/or scattered by the target droplet DP. Thus,the droplet detection module 420 detects when a target droplet haspassed position P.

The time, t₀, at which the droplet detection module 420 detects thetarget droplet DP passing the position P is provided to a timing andenergy measurement module 430. Once the target droplet reaches the zoneof excitation ZE and is heated with an excitation laser pulse LR2, thematerial of the target droplet is ionized into plasma, which emits EUVradiation EUV. This EUV radiation is detected by the timing and energymeasurement module (TEM) 430.

In an embodiment, the timing and energy measurement module 430 includesa detector configured to detect the EUV power generated at each instanceof plasma generation. The detector includes a photodiode or a filteredphotodiode configured to convert the energy from photons incident on itinto an electrical signal in some embodiments. In an embodiment, thedetector also includes a mirror that reflects the EUV radiation from afixed position in the exposure tool on to the photodiode.

The timing and energy measurement module 430, in an embodiment, isconfigured to estimate the time at which the power of the EUV radiationpeaks, t_(rad). The speed of the target droplet is then used to triggerthe excitation pulse for a subsequent target droplet. Those of skill inthe art would appreciate that in order to estimate the time at which EUVpower peaks, it is not necessary to measure the absolute power EUV powergenerated at every instance of plasma generation, rather the rate ofchange of EUV power is sufficient to estimate the precise time at whichthe EUV power peaks.

Speed of a target droplet is calculated based on a peak in the EUVenergy, and this measurement of speed is used to trigger an excitationpulse for the next target droplet. In an embodiment, the timing andenergy measurement module 430 is further configured to calculate theprecise time at which the next target droplet will arrive at the zone ofexcitation ZE, and provide a trigger signal to the excitation lasersource 300 to control the trigger time for the excitation pulse LR2.

In the LPP EUV radiation source apparatus as set forth above, some ofthe laser pulses of the excitation laser LR2 do not hit the targetdroplet and merely pass through the zone of excitation ZE. In someembodiments, the missed excitation laser LR2 is scattered by scatteringoptics 190, and the scattered excitation laser heats vanes of the debriscollection mechanisms 150 to melt tin debris deposited on the vanes.

Productivity of wafer manufacturing in a semiconductor manufacturingoperation relates to the input EUV energy on wafer (EUV dosage) and theconversion efficiency of the laser-plasma interaction between theexcitation laser and the tin droplets. An increase of the EUV energy isachievable by raising the excitation laser power, which may increaseelectrical power usage. In the present disclosure, the excitation laser,which hits and/or misses the tin droplets, is reused, and is directed tothe zone of excitation to hit the tin droplet again. The excitationlaser is collected by one or more mirrors after passing through the zoneof excitation inside the vessel and refocused on the droplet/plasma toenhance the conversion efficiency and reduce the debris production.

FIG. 2 shows a schematic configuration of an LPP EUV radiation sourceaccording to an embodiment of the present disclosure. Materials,configuration, parts, components, structures, and/or operationsexplained with respect to FIGS. 1A-1C are also employed in the followingembodiments and the detailed explanation may be omitted.

As shown in FIG. 2 , one or more mirrors that reflect the excitationlaser LR2 are disposed inside the vacuum vessel of the LPP EUV radiationsource. In some embodiments, a first mirror 510 and a second mirror 520are disposed. The first mirror is located between the zone of excitationZE and the output port 160 of the EUV radiation source along the Zdirection, which is the initial direction of the excitation laser LR2.The first mirror located in the Z direction can prevent the excitationlaser from emitting from the output port and prevent the opticalcomponents of the EUV scanner from being damaged. The second mirror 520is located along the −X direction from the first mirror 510 (12 o'clockposition), where the +X direction is the travel direction of the tindroplet from the droplet generator 115. The first mirror 510 and thesecond mirror 520 have a reflection surface made of a Cu or a Cu alloylayer formed on a mirror body. In other embodiments, the mirrors aremade of Cu or a Cu alloy. In some embodiments, the diameter of the firstand second mirrors is about 1 cm to about 15 cm in some embodiments.

In some embodiments, at least one of the first mirror 510 and the secondmirror 520 is a concave mirror that reflects and focuses the excitationlaser LR2 passing through the zone of excitation ZE. In someembodiments, at least one of the first mirror 510 and the second mirror520 is a flat mirror that merely reflects the excitation laser LR2.

In some embodiments, the excitation laser LR2 passing through the zoneof excitation ZE is reflected by the first mirror 510 and is directed tothe second mirror 520. As set forth above, in some embodiments, thereflected laser by the first mirror 510 focuses on the second mirror520. Then, the reflected excitation laser is further reflected by thesecond mirror 520 and is directed to the zone of excitation ZE. In someembodiments, the reflected laser by the second mirror 520 focuses at thezone of excitation.

In some embodiments, the excitation laser reflected by the second mirror520 is further directed to a part of the vessel or a component of theEUV radiation source apparatus. In some embodiments, the excitationlaser reflected by the second mirror 520 is further directed to thedroplet catcher 120 to heat the droplet catcher 120. In someembodiments, at least the entrance port of the droplet catcher 120 isirradiated with the excitation laser.

In some embodiments, a controller 550 is coupled to the first and/orsecond mirrors to control the positions, angles and any other parametersof the mirrors. In some embodiments, the first and/or second mirrors areconfigured to be movable by an adjusting mechanism, which includes oneor more of an actuator (e.g. piezo actuator), a motor, a piston, a gear,or any other mechanical or electrical parts. Further, in someembodiments, one or more sensors 530 are installed inside the vessel tomonitor the excitation laser and/or the vessel interior. In someembodiments, the sensor 530 includes a camera or a thickness measurementdevice.

FIG. 3 shows a diagram explaining a reuse of excitation laser LR2according to an embodiment of the present disclosure. As set forthabove, the excitation laser includes a pre-pulse laser and a main pulselaser.

In case of the pre-pulse laser irradiation, the excitation laserinitially directed to the zone of excitation ZE hits a tin droplet,which causes the tin droplet to expand into a pancake shape. Since thesize of the excitation laser is greater than the size of the tindroplet, most or some of the excitation laser passes through the zone ofexcitation and is directed to the first mirror 510. The excitation laseris then reflected by the first and second mirrors, and is directed backto the zone of excitation to irradiate the tin droplet again, as shownin FIG. 3 . In some embodiments, the same tin droplet is irradiated bythe same laser pulse, i.e., the initial laser pulse and the reflectedlaser pulse.

Similarly, in case of the main-pulse laser irradiation, the excitationlaser initially directed to the zone of excitation ZE hits thepancake-shaped tin droplet, which makes the tin droplet into plasma. Theexcitation laser is then reflected by the first and second mirrors, andis directed back to the zone of excitation to irradiate the tin dropletagain, as shown in FIG. 3 . In some embodiments, the same tin droplet isirradiated by the same laser pulse, i.e., the initial laser pulse andthe reflected laser pulse.

In some embodiments, the focal point of the reflected excitation laseris slightly different from the focal point of the initial excitationlaser to account for a time delay caused by the excitation lasertraveling from the zone of excitation and back to the zone of excitationvia the first and second mirrors. The difference is about 10 nm to 10 μmalong the +X direction in some embodiments. In some embodiments, thetime delay is measured by the droplet illumination module (DIM) 410and/or the droplet detection module (DDM) 420 shown in FIG. 1C, and atleast one of the first and second mirrors is adjusted by the controller550 so as to adjust the focal point of the reflected excitation laser.

FIGS. 4A-4E show configurations of mirrors in accordance with variousembodiments of the present disclosure. Materials, configurations, parts,components, structures, and/or operations explained with respect toFIGS. 1A-3 are also employed in the following embodiments and thedetailed explanation may be omitted.

In some embodiments, the reflected excitation laser from the secondmirror 520 does not pass through the zone of excitation again, but isdirected to a part or a component inside the vessel, to locally heat thepart or the component, as shown in FIGS. 4A and 4B. In some embodiments,the reflected excitation laser is directed to the vane 150 of the debriscollection mechanism to melt deposited tin debris thereon, as shown inFIG. 4A. In other embodiments, the reflected excitation laser isdirected to the collector mirror 110 to melt deposited tin debristhereon, as shown in FIG. 4B. In some embodiments, the controllercontrols the excitation light source 300 to adjust (e.g., reduce) outputlaser power to minimize damage on the collector mirror.

In FIG. 4C, in some embodiments, the second mirror 520 is located atother than the 12 o'clock position, for example, the 6 o'clock positionso that the reflected excitation laser is directed to −X direction. InFIG. 4D, in some embodiments, no second mirror is used and the firstmirror is controlled to direct the reflected excitation laser to adesired location inside the vessel.

Further, in some embodiments, as shown in FIG. 4E, a third mirror 540 islocated at the 6 o'clock position or nearby, to direct the reflectedexcitation laser that passes the zone of excitation twice to a desiredlocation.

In some embodiments, the sensor 530 is configured to detect depositionof the tin debris inside the vessel. As set forth above, the sensor 530includes a camera in some embodiments, the camera monitors thedeposition of the tin debris. In some embodiments, the camera is movableto scan the inside the vessel. When the deposition of the tin debris isexcessive (e.g., greater than a threshold amount in terms of e.g., areaor thickness), the controller 550 controls one or more of the first andsecond mirrors to direct the reflected excitation laser toward the areawhere the excessive tin debris is deposited.

In some embodiments, the heating and melting operation by the reflectedexcitation laser is performed without generating the tin droplets, as apart of cleaning and/or maintenance operation of the EUV radiationsource. In some embodiments, at least one of the first mirror 510 or thesecond mirror 520 is controlled to scan the reflected radiation laserinside the vessel so that various locations inside the vessel is heated.

FIG. 5 shows a flowchart of a method of making a semiconductor device,and FIGS. 6A, 6B, 6C and 6D show a sequential manufacturing operation ofthe method of making a semiconductor device in accordance withembodiments of the present disclosure. A semiconductor substrate orother suitable substrate to be patterned to form an integrated circuitthereon is provided. In some embodiments, the semiconductor substrateincludes silicon. Alternatively or additionally, the semiconductorsubstrate includes germanium, silicon germanium or other suitablesemiconductor material, such as a Group III-V semiconductor material. AtS501 of FIG. 5 , a target layer to be patterned is formed over thesemiconductor substrate. In certain embodiments, the target layer is thesemiconductor substrate. In some embodiments, the target layer includesa conductive layer, such as a metallic layer or a polysilicon layer; adielectric layer, such as silicon oxide, silicon nitride, SiON, SiOC,SiOCN, SiCN, hafnium oxide, or aluminum oxide; or a semiconductor layer,such as an epitaxially formed semiconductor layer. In some embodiments,the target layer is formed over an underlying structure, such asisolation structures, transistors or wirings. At S502, of FIG. 5 , aphoto resist layer is formed over the target layer, as shown in FIG. 6A.The photo resist layer is sensitive to the radiation from the exposingsource during a subsequent photolithography exposing process. In thepresent embodiment, the photo resist layer is sensitive to EUV lightused in the photolithography exposing process. The photo resist layermay be formed over the target layer by spin-on coating or other suitabletechniques. The coated photo resist layer may be further baked to driveout solvent in the photo resist layer. At S503 of FIG. 5 , thephotoresist layer is patterned using an EUV reflective mask, as shown inFIG. 6B. The patterning of the photoresist layer includes performing aphotolithography exposing process by an EUV exposing system includingthe LPP EUV radiation source of the present disclosure, using the EUVmask. During the exposing process, the integrated circuit (IC) designpattern defined on the EUV mask is imaged to the photoresist layer toform a latent pattern thereon. The patterning of the photoresist layerfurther includes developing the exposed photoresist layer to form apatterned photoresist layer having one or more openings. In oneembodiment where the photoresist layer is a positive tone photoresistlayer, the exposed portions of the photoresist layer are removed duringthe developing process. The patterning of the photoresist layer mayfurther include other process steps, such as various baking steps atdifferent stages. For example, a post-exposure-baking (PEB) process maybe implemented after the photolithography exposing process and beforethe developing process.

At S504 of FIG. 5 , the target layer is patterned utilizing thepatterned photoresist layer as an etching mask, as shown in FIG. 6C. Insome embodiments, the patterning the target layer includes applying anetching process to the target layer using the patterned photoresistlayer as an etch mask. The portions of the target layer exposed withinthe openings of the patterned photoresist layer are etched while theremaining portions are protected from etching. Further, the patternedphotoresist layer may be removed by wet stripping or plasma ashing, asshown in FIG. 6D.

FIG. 7 illustrates a flow diagram of an exemplary process 700 foroperating an LPP EUV radiation source apparatus in accordance with someembodiments of the disclosure. The process 700 or a portion of theprocess 700 may be performed by the LPP EUV radiation apparatus asdescribed in this disclosure. In some embodiments, the process 700 or aportion of the process 700 is performed and/or is controlled by thecomputer system 900, which includes or is a part of the controller 550,described below with respect to FIGS. 9A and 9B. In some embodiments,the process 700 or a portion of the process 700 is performed by thecontrol system 800, which includes or is a part of the controller 550,of FIG. 8 described below. The method includes an operation S710, wherean excitation laser emitted from a laser light source is introduced intothe EUV light source.

In operation S720, the excitation laser is reflected by a first mirror.In some embodiments, the excitation laser hits a tin droplet before itis reflected by the first mirror. In other embodiments, no tin dropletis generated and thus the excitation laser merely passes through thezone of excitation.

In operation S730, the excitation laser reflected by the first mirror isfurther reflected by a second mirror. In operation S740, the excitationlaser reflected by the second mirror is directed to the zone ofexcitation to irradiate the tin droplet, and/or to locally heat a part,a component or a location inside the EUV radiation source apparatus.

FIG. 8 shows a control system 800 for operating an LPP EUV radiationsource apparatus in accordance with some embodiments of the presentdisclosure. The control system 800 includes a main controller 810, whichincludes or is a part of the controller 550, one or more sensors 530, afirst mirror 510 and a second mirror 520 coupled to the main controller810. The main controller 810 is further coupled to the droplet generator115 and/or the excitation laser source 300 in some embodiments.

In some embodiments, the controller is configured to control the secondmirror to adjust the reflection of the excitation laser based on amonitoring result of the sensor. In some embodiments, when the sensordetects an excessive debris deposition above a threshold, the controlleris configured to control the second mirror to direct the excitationlaser reflected by the second mirror to the excessive debris deposition.In some embodiments, the controller is configured to control the firstmirror to adjust the reflection of the excitation laser. In someembodiments, the controller is configured to control the second mirrorto locally heat inside the EUV light source apparatus. In someembodiments, the controller stops the operation of the dropletgenerator, and controls the first and/or second mirror to locally heatthe inside of the vessel with the reflected excitation laser. In someembodiments, the controller controls the excitation light source 300 toadjust the output laser power.

FIGS. 9A and 9B illustrate an apparatus for operating an LPP EUVradiation source apparatus in accordance with some embodiments of thepresent disclosure. In some embodiments, the computer system 900 is usedfor performing the functions of the modules of FIG. 8 . In someembodiments, the computer system 900 is used to execute the process 700of FIG. 7 .

FIG. 9A is a schematic view of a computer system that performs thefunctions of operating an LPP EUV radiation source apparatus. All of ora part of the processes, method and/or operations of the foregoingembodiments can be realized using computer hardware and computerprograms executed thereon. In FIG. 9A, a computer system 900 is providedwith a computer 901 including an optical disk read only memory (e.g.,CD-ROM or DVD-ROM) drive 905 and a magnetic disk drive 906, a keyboard902, a mouse 903, and a monitor 904.

FIG. 9B is a diagram showing an internal configuration of the computersystem 900. In FIG. 9B, the computer 901 is provided with, in additionto the optical disk drive 905 and the magnetic disk drive 906, one ormore processors, such as a micro processing unit (MPU) 911, a ROM 912 inwhich a program such as a boot up program is stored, a random accessmemory (RAM) 913 that is connected to the MPU 911 and in which a commandof an application program is temporarily stored and a temporary storagearea is provided, a hard disk 914 in which an application program, asystem program, and data are stored, and a bus 915 that connects the MPU911, the ROM 912, and the like. The computer 901 may include a networkcard (not shown) for providing a connection to a LAN.

The program for causing the computer system 900 to execute the functionsfor operating an LPP EUV radiation source apparatus in the foregoingembodiments may be stored in an optical disk 921 or a magnetic disk 922,which are inserted into the optical disk drive 905 or the magnetic diskdrive 906, and transmitted to the hard disk 914. Alternatively, theprogram may be transmitted via a network (not shown) to the computer 901and stored in the hard disk 914. At the time of execution, the programis loaded into the RAM 913. The program may be loaded from the opticaldisk 921 or the magnetic disk 922, or directly from a network. Theprogram does not necessarily have to include, for example, an operatingsystem (OS) or a third party program to cause the computer 901 toexecute the functions of the control system for operating an LPP EUVradiation source apparatus in the foregoing embodiments. The program mayonly include a command portion to call an appropriate function (module)in a controlled mode and obtain desired results.

Embodiments of the present disclosure are directed to improvingefficiency of the usage of an excitation laser in an LPP EUV lightsource apparatus. By reflecting the excitation laser after hitting ametal droplet or passing through a zone of excitation, and reusing theexcitation laser to generate metal plasma and/or to locally heat theinside the LPP EUV light source apparatus, it is possible improveoperation efficiency of the excitation laser source and to reducedeposition of metal debris inside the LPP EUV light source apparatus.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

According to some embodiments of the present disclosure, an extremeultra violet (EUV) light source apparatus includes a metal dropletgenerator, a collector mirror, an excitation laser inlet port forreceiving an excitation laser, a first mirror configured to reflect theexcitation laser that passes a zone of excitation, and a second mirrorconfigured to reflect the excitation laser reflected by the firstmirror. In one or more of the foregoing or following embodiments, thesecond mirror is configured such that the excitation laser reflected bythe second mirror passes the zone of excitation. In one or more of theforegoing or following embodiments, the EUV light source apparatusfurther includes a metal droplet catcher. The second mirror isconfigured such that the metal droplet catcher is irradiated with theexcitation laser reflected by the second mirror. In one or more of theforegoing or following embodiments, the first mirror and the secondmirror are configured such that the excitation laser reflected by thesecond mirror hits a metal droplet that is hit by the excitation laserbefore reflected by the first mirror. In one or more of the foregoing orfollowing embodiments, the second mirror is configured such that theexcitation laser reflected by the second mirror does not pass the zoneof excitation. In one or more of the foregoing or following embodiments,the EUV light source apparatus further includes a debris collectionmechanism, and the second mirror is configured such that the excitationlaser reflected by the second mirror is directed to a part of the debriscollection mechanism. In one or more of the foregoing or followingembodiments, the second mirror is configured such that the excitationlaser reflected by the second mirror is directed to the collectormirror. In one or more of the foregoing or following embodiments, atleast one of the first mirror or the second mirror is a convex mirror.In one or more of the foregoing or following embodiments, at least oneof the first mirror or the second mirror is a flat mirror. In one ormore of the foregoing or following embodiments, the first mirror and thesecond mirror have a reflection surface made of Cu or a Cu alloy.

According to some embodiments of the present disclosure, an EUV lightsource apparatus includes a metal droplet generator, a collector mirror,an excitation laser inlet port for receiving an excitation laser, afirst mirror configured to reflect the excitation laser that passes azone of excitation, a second mirror configured to reflect the excitationlaser reflected by the first mirror, and a controller configured tocontrol the second mirror to adjust reflection of the excitation laser.In one or more of the foregoing or following embodiments, the EUV lightsource apparatus further includes a sensor configured to monitor ordetect deposition of metal debris, and the controller is configured tocontrol the second mirror to adjust the reflection of the excitationlaser based on a monitoring result of the sensor. In one or more of theforegoing or following embodiments, the sensor is a camera. In one ormore of the foregoing or following embodiments, when the sensor detectsan excessive debris deposition above a threshold, the controller isconfigured to control the second mirror to direct the excitation laserreflected by the second mirror to the excessive debris deposition. Inone or more of the foregoing or following embodiments, the controller isconfigured to control the first mirror to adjust the reflection of theexcitation laser. In one or more of the foregoing or followingembodiments, the controller configured to control the second mirror tolocally heat inside the EUV light source apparatus. In one or more ofthe foregoing or following embodiments, the controller configured tocontrol the second mirror to locally heat inside the EUV light sourceapparatus when the metal droplet generator is not operating.

According to some embodiments of the present disclosure, in a method ofoperating an EUV light source apparatus, an excitation laser emittedfrom a laser light source is introduced into the EUV light source, theexcitation laser is reflected by one or more mirrors, and inside the EUVlight source apparatus is locally heated by the excitation laserreflected by the one or more mirrors. In one or more of the foregoing orfollowing embodiments, the excitation laser is reflected by a firstmirror and the excitation laser reflected by the first mirror isreflected by a second mirror. The inside the EUV light source apparatusis locally heated by the excitation laser reflected by the secondmirror. In one or more of the foregoing or following embodiments, theexcitation laser reflected by the second mirror passes through a zone ofexcitation of the EUV light source. In one or more of the foregoing orfollowing embodiments, the excitation laser reflected by the secondmirror does not pass through a zone of excitation of the EUV lightsource. In one or more of the foregoing or following embodiments, theinterior portion is one of a droplet catcher, a debris collectionmechanism or a collector mirror.

According to some embodiments of the present disclosure, in a method ofoperating an EUV light source apparatus, the EUV light source includes,a metal droplet generator, a collector mirror, an excitation laser inletport for receiving an excitation laser, a first mirror and a secondmirror. The excitation laser is introduced from the inlet port, theexcitation laser that passes through a zone of excitation is reflectedby the first mirror, and the excitation laser reflected by the firstmirror is further reflected by the second mirror. In one or more of theforegoing or following embodiments, the excitation laser reflected bythe second mirror is directed to pass through the zone of excitation. Inone or more of the foregoing or following embodiments, the excitationlaser reflected by the second mirror is directed to hit a metal dropletcatcher. In one or more of the foregoing or following embodiments, thefirst mirror and the second mirror are configured such that theexcitation laser reflected by the second mirror hits a metal dropletthat is hit by the excitation laser before the excitation laser isreflected by the first mirror. In one or more of the foregoing orfollowing embodiments, the excitation laser reflected by the secondmirror is directed not to pass through the zone of excitation. In one ormore of the foregoing or following embodiments, the excitation laserreflected by the second mirror is directed to hit a part of a debriscollection mechanism. In one or more of the foregoing or followingembodiments, the excitation laser reflected by the second mirror isdirected to hit the collector mirror.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

1. An extreme ultra violet (EUV) light source apparatus, comprising: acollector mirror; an excitation laser inlet port configured to receivean excitation laser; a first mirror configured to reflect the excitationlaser that passes through a zone of excitation; and a second mirrorconfigured to reflect the excitation laser reflected by the firstmirror.
 2. The EUV light source apparatus of claim 1, wherein the secondmirror configured to reflect the excitation laser reflected by the firstmirror toward the zone of excitation.
 3. The EUV light source apparatusof claim 2, wherein the second mirror configured to focus the excitationlaser reflected by the first mirror at the zone of excitation.
 4. TheEUV light source apparatus of claim 1, wherein the second mirrorconfigured to reflect the excitation laser reflected by the first mirrortoward the collector mirror.
 5. The EUV light source apparatus of claim1, wherein the second mirror configured to reflect the excitation laserreflected by the first mirror toward a metal droplet catcher.
 6. The EUVlight source apparatus of claim 5, wherein the second mirror configuredto reflect the excitation laser reflected by the first mirror toward themetal droplet catcher after passing through the zone of excitation. 7.The EUV light source apparatus of claim 1, wherein the second mirrorconfigured to reflect the excitation laser reflected by the first mirrortoward a debris collection mechanism.
 8. The EUV light source apparatusof claim 1, wherein at least one of the first mirror or the secondmirror is a flat mirror.
 9. An extreme ultra violet (EUV) light sourceapparatus, comprising: a collector mirror; an excitation laser inletport configured to receive an excitation laser; a first mirrorconfigured to reflect the excitation laser that passes through a zone ofexcitation; a second mirror configured to reflect the excitation laserreflected by the first mirror; and a third mirror configured to reflectthe excitation laser reflected by the second mirror.
 10. The EUV lightsource apparatus of claim 9, wherein the second mirror configured toreflect the excitation laser reflected by the first mirror toward thezone of excitation.
 11. The EUV light source apparatus of claim 10,wherein the second mirror configured to focus the excitation laserreflected by the first mirror at the zone of excitation.
 12. The EUVlight source apparatus of claim 9, wherein the third mirror configuredto reflect the excitation laser reflected by the first mirror toward adebris collection mechanism.
 13. The EUV light source apparatus of claim9, further comprising a controller configured to control at least one ofthe first mirror or the second mirror.
 14. The EUV light sourceapparatus of claim 13, further comprising a sensor configured to monitoror detect deposition of metal debris, wherein the controller isconfigured to control at least one of the first mirror or the secondmirror based on a monitoring result of the sensor.
 15. The EUV lightsource apparatus of claim 13, wherein the sensor is a camera.
 16. TheEUV light source apparatus of claim 13, wherein when the sensor detectsan excessive debris deposition above a threshold, the controller isconfigured to control the at least one of the first mirror or the secondmirror to direct the excitation laser reflected by the second mirror tothe excessive debris deposition.
 17. The EUV light source apparatus ofclaim 13, wherein the controller configured to control at least one ofthe first mirror or the second mirror to locally heat an interiorportion of the EUV light source apparatus.
 18. The EUV light sourceapparatus of claim 13, wherein at least one of the first mirror or thesecond mirror is a flat mirror.
 19. An extreme ultra violet (EUV) lightsource apparatus, comprising: a collector mirror; an excitation laserinlet port configured to receive an excitation laser; a first mirrorconfigured to reflect the excitation laser that passes through a zone ofexcitation toward a target location inside the EUV light sourceapparatus.
 20. The EUV light source apparatus of claim 19, furthercomprising a controller configured to control the first mirror to changethe target location.